Geared motors are used in many areas of mechanical engineering in order to generate rotary or linear movements. Electric motors are typically operated at relatively high rotational speeds, even though only a relatively low torque is generated. A transmission can reduce the rotational speed in a suitable ratio, the torque being increased correspondingly.
Electric motors having a transmission are often used in conveying technology in order to drive rollers or conveyors either directly or by means of belts, in particular toothed belts.
In applications in which there is only a small amount of space available and/or specific requirements in respect of cleanliness and hygiene have to be met, conventional geared motors cannot be used in optimum fashion. They often require too much space and/or they cannot be cleaned with a justifiable level of outlay. For such applications, use is often made of so-called drum motors, as are described, for example in WO 2013/143550 A1. Such drives are very compact, because the free volume within a drum is used to accommodate an electric motor and an associated transmission. The torque is generated within the drum and transmitted to the drum in order thus to drive a load. Drum motors therefore have a fixed inner shaft with a drum which rotates about the shaft and in which the drive is accommodated. This requires an electrical supply line, which is generally routed within the fixed shaft. The task of sealing the same in relation to oil, which can creep along the supply line, is difficult and can give rise to hygiene-related problems if used in the food industry.
Furthermore, GB 2472020 A discloses a drum motor which has an outer stator and an inner rotor and in which the stator and rotor are provided within the drum.
Moreover, a further fundamental problem is the fact that the electric motor has available only a relatively small diameter within the drum, the rotor and stator of the electric motor having to be accommodated within said diameter. This means, in general terms, that only a relatively low torque can be generated, since the electric-motor torque which can be generated increases approximately in proportion with the square of the diameter of the electric motor. It is also the case in an electric motor that increasing power gives rise to more and more heat, which has to be dissipated, this only being possible in practice, in the case of drum motors, via the surface of the drum, and this place pronounced limitations on the power of the electric motor in the interior of the drum.